A prior art method for installing the guide rails, such as the car guide rails and/or counterweight guide rails, of an elevator in the elevator shaft or similar. In the prior art method, to which reference is made in the description of the prior art in publication U.S. Pat. No. 6,422,352, the guide rails are installed by assembly in stages, starting from the bottom of the elevator shaft, by placing guide rail sections that are shorter than the whole length of the guide rail one consecutively after the other and by aligning the guide rail sections vertically by means of a perpendicular laser beam produced by a direction laser. In addition it has been necessary to use plumb lines suspended from the machine room above the shaft, from floor levels or a from separate scaffold. Likewise a prior art system for assembling guide rails in the elevator shaft from consecutive guide rail sections, which system comprises a direction laser, which produces a perpendicular laser beam for aligning the guide rail sections.
In prior art high-precision lasers are used with long distances as a direction laser, the shaped laser beam produced by which is intended to remain as a distinct narrow bunch over a long distance, so that it can be utilized in installation for the entire length of the elevator shaft.
The use of lasers in installing elevator guide rails is not widespread because the dust hanging in the air of the elevator shaft is a problem, due to which the laser beam bunch disperses over a long distance and does not achieve a distinct round lighting point, by means of which accurate alignment can be performed. Another problem is that long-distance lasers are quite expensive in price and large in size. The accuracy of a plumb line, for its part, is affected by air currents and temperature fluctuations.